docs: add Batch transaction exports to HISTORY.md

Author: nabe3m

packages/xrpl/HISTORY.md

@@ -4,6 +4,9 @@ Subscribe to [the **xrpl-announce** mailing list](https://groups.google.com/g/xr
 
 ## Unreleased
 
+### Added
+* Export `Batch` (XLS-56) transaction types and utilities
+
 ### Fixed
 * Fix incorrect type checking in `validateVaultCreate` that prevented vault creation with MPT as an asset.